The present invention relates to an antenna for a mobile communications terminal, and more particularly, to a multi-frequency antenna capable of communicating signals having a plurality of frequencies: used for mobile phones and data communications, etc.
In recent years, the mobile communication has made a rapid progress. Especially, the mobile phones have significantly come into widespread use, and reduction in size and weight have been achieved. In case of the mobile phone, a dual band is becoming a main stream in respective areas of the world, for example, PDC (Personal Digital Cellular) 800 MHz band and PDC 1.5 GHz band in Japan, GSM (Global System for Mobile Communications) 900 MHz band and GSM 1.8 GHz band in Europe, and AMPS (Advanced Mobile Phone Service) 800 MHz band and PCS (Personal Communication Services) 1.9 GHz band in North America. In addition, communication systems such as GPS (Global Positioning System) of 1.5 GHz band, Bluetooth of 2.4 GHz band, IMT (International Mobile Telecommunication) 2000 of 2 GHz band are becoming widespread. Under the circumstances, in order to conduct these mobile phones and communication systems in a single apparatus for the mobile communications, antennas adapted to respective frequency bands need to be provided in the single apparatus.
FIG. 8 shows a first related-art in which an apparatus incorporates an antenna for the dual band of AMPS/PCS for the mobile phone and an antenna for the GPS. Such a configuration is disclosed in International Patent Publication No. WO 02/89249.
A carrier 12 made of dielectric substance is disposed on a substrate 10, and a first antenna element 14 for the dual band of AMPS/PCS made of sheet metal is disposed on an upper face of this carrier 12. Further, a second antenna element 16 for the GPS made of sheet metal is disposed on a side face of the carrier 12. Numerals 14a and 14b designate a power supply terminal and a grounding terminal of the first antenna element 14, respectively. Numerals 16a and 16b designate a power supply terminal and a grounding terminal of the second antenna element 16, respectively.
FIG. 9 shows a second related-art apparatus incorporating an antenna for the dual band for the mobile phone and an antenna for the GPS. The elements similar to those in the first related-art will be designated by the same reference numerals, and repetitive explanations will be omitted.
In this example, a carrier 12 which is smaller than the carrier shown in FIG. 8 is disposed on a substrate 10, and a first antenna element 14 for the dual band made of sheet metal is disposed on an upper face of the carrier 12. Further, a second antenna element 16 for the GPS made of sheet metal or conductive foil is disposed on the substrate 10 near the carrier 12, along two side faces of the carrier 12.
FIG. 10 shows a third related-art apparatus incorporating an antenna for the dual band for the mobile phone and an antenna for the GPS. The elements similar to those in the first related-art will be designated by the same reference numerals, and repetitive explanations will be omitted.
In this example, a carrier 12 which is smaller than the carrier shown in FIG. 8 is disposed on a substrate 10, and a first antenna element 14 for the dual band made of sheet metal is disposed on an upper face of the carrier 12. Further, a ceramic antenna 18 for the GPS is disposed on the substrate 10 near the carrier 12.
In the first related-art shown in FIG. 8, high gain can be obtained, because the structure is simple and the first antenna element 14 has a large area. However, the largest point of electric voltage of the second antenna element 16 is located close to the first antenna element 14, and also, the largest point of electric voltage of the first antenna element 14 is located close to the second antenna element 16. For this reason, interference occurs between them, which will make isolation worse. Because of the worse isolation, there has been such disadvantage that the gain and the voltage standing wave ratio (VSWR) may be decreased. In view of the above, it has been considered that the signals to be received by the first and second antenna elements 14, 16 should be separated by a filter. However, this leads to a problem that an area for mounting the filter and cost for components are required.
In the second related-art shown in FIG. 9, the first and second antenna elements 14, 16 can be disposed relatively spaced from each other, and the isolation can be improved, enabling the gain and VSWR to be enhanced in this respect. However, the substrate 10 to be incorporated in the mobile phone or the like has a limited size, and so, in order to provide the second antenna element 16 on the substrate 10, the area of the first element 14 must be made smaller than that in the first related-art shown in FIG. 8. Consequently, the gain will be inevitably decreased, because the area of the first antenna element 14 has been made smaller.
In the third related-art shown in FIG. 10, the first antenna element 14 and the ceramic antenna 18 must be sufficiently spaced from each other in order to eliminate interference between them, and for this reason, the area of the first antenna element 14 will be made smaller, resulting in decrease of the gain. Moreover, because the ceramic antenna 18 has a high Q value, even a slight deviation of resonant frequency of the ceramic antenna 18 from the frequency of the GPS signal which is being received will cause a remarkable drop of the gain. Further, because the resonant frequency of the ceramic antenna 18 will be largely affected by metallic conductors in surrounding areas, it is necessary to check the resonant frequency of the ceramic antenna 18, in a state where other circuit components in addition to the first antenna element 14 and the ceramic antenna 18 have been mounted on the substrate 10. This will be a disadvantage when a trouble has happened. Still further, in case where a terminal of the ceramic antenna 18 is fixed by soldering to the conductive foil on the substrate 10 and electrically connected thereto, there is an anxiety that the soldered foil may be removed from the substrate 10 with vibrations or shocks, and reliability will be lost in both electrical and mechanical features.